Init commit with many years of arduino sketches and projects. I dont know if the esp8266 includes much, but there are also libraries. I hope they dont have crazy automatic versioning through the Arduino IDE.

Projects/libraries/Installed_libs/Time/Examples/TimeRTCSet/TimeRTCSet.pde

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+/*
+ * TimeRTCSet.pde
+ * example code illustrating Time library with Real Time Clock.
+ *
+ * RTC clock is set in response to serial port time message 
+ * A Processing example sketch to set the time is inclided in the download
+ */
+
+#include <Time.h>  
+#include <Wire.h>  
+#include <DS1307RTC.h>  // a basic DS1307 library that returns time as a time_t
+
+
+void setup()  {
+  Serial.begin(9600);
+  setSyncProvider(RTC.get);   // the function to get the time from the RTC
+  if(timeStatus()!= timeSet) 
+     Serial.println("Unable to sync with the RTC");
+  else
+     Serial.println("RTC has set the system time");      
+}
+
+void loop()
+{
+  if(Serial.available())
+  {
+     time_t t = processSyncMessage();
+     if(t >0)
+     {
+        RTC.set(t);   // set the RTC and the system time to the received value
+        setTime(t);          
+     }
+  }
+   digitalClockDisplay();  
+   delay(1000);
+}
+
+void digitalClockDisplay(){
+  // digital clock display of the time
+  Serial.print(hour());
+  printDigits(minute());
+  printDigits(second());
+  Serial.print(" ");
+  Serial.print(day());
+  Serial.print(" ");
+  Serial.print(month());
+  Serial.print(" ");
+  Serial.print(year()); 
+  Serial.println(); 
+}
+
+void printDigits(int digits){
+  // utility function for digital clock display: prints preceding colon and leading 0
+  Serial.print(":");
+  if(digits < 10)
+    Serial.print('0');
+  Serial.print(digits);
+}
+
+/*  code to process time sync messages from the serial port   */
+#define TIME_MSG_LEN  11   // time sync to PC is HEADER followed by unix time_t as ten ascii digits
+#define TIME_HEADER  'T'   // Header tag for serial time sync message
+
+time_t processSyncMessage() {
+  // return the time if a valid sync message is received on the serial port.
+  while(Serial.available() >=  TIME_MSG_LEN ){  // time message consists of a header and ten ascii digits
+    char c = Serial.read() ; 
+    Serial.print(c);  
+    if( c == TIME_HEADER ) {       
+      time_t pctime = 0;
+      for(int i=0; i < TIME_MSG_LEN -1; i++){   
+        c = Serial.read();          
+        if( c >= '0' && c <= '9'){   
+          pctime = (10 * pctime) + (c - '0') ; // convert digits to a number    
+        }
+      }   
+      return pctime; 
+    }  
+  }
+  return 0;
+}
+